Multilayer optical film can include oriented layers that can be semi-crystalline and the birefringence of these layers provides large increases in the optical power over isotropic polymeric multilayers. Heating these multilayer optical films can at least partially melt the oriented material in order to reduce or remove the birefringence of the oriented optical layers, resulting in a reduction in the optical power of their reflection bands. In one useful case, the multilayer optical films include an infrared light absorbing dye or pigment. These multilayer optical films can thus absorb radiant energy, e.g. of an infrared light laser, selectively melting the oriented material in the optical packet containing the absorber, and reducing the reflectivity of that optical packet. Images can be constructed by selective exposure of the infrared light to the multilayer optical films. In this manner, controlled spatial patterning of the reflectivity across the multilayer optical film can be accomplished.
Simple addition of the un-dispersed infrared light absorber in powder form to the film resin can lead to process disruptions and reduced film quality. For example, large particles can cause flow defects that manifest as streaks, mottling, parabolically shaped flow lines or other marks, disrupting the uniformity, appearance and/or the performance of the cast and also drawn film. The variability of infrared light absorber within the film leads to uncertainty in the radiation exposure conditions needed for selective melting and imaging of the multilayer optical film, leading to under-heating or over-heating portions of the film. Localized over-heating of the infrared light absorber by a high-energy-flux laser results in charring and other defects in the imaged film.